Reduced glutathione (γ-L-glutamyl-L-cysteinyl-glycine) is a substance occurring in a wide range of living organisms, and is known to have a detoxification effect in the liver, in addition to acting as a coenzyme. This has made reduced glutathione useful in a wide range of applications including products such as pharmaceuticals, health-aid food, and cosmetics, and raw materials, intermediates, or the like of such products.
For ease of handling, a powder is the desired form of reduced glutathione used for such products, raw materials, and intermediates. However, the noncrystalline (amorphous) form of reduced glutathione obtained through a common dry powder manufacturing method such as freeze drying and spray drying has high hygroscopicity and insufficient fluidity, and is not suited for processing.
A crystal of a free form of reduced glutathione is known (Patent Document 1). However, free-form crystals have low solubility, and are not suited for liquid preparations. The acidic nature of free-form crystals also requires care for processing. This has created a demand for a crystal of reduced glutathione that has good preservation stability, and is easy to process.
A monohydrate (Patent Document 2) and a hexahydrate (Patent Document 3) of a free oxidized glutathione (a dimer of glutathione) with a disulfide linkage between reduced glutathione molecules are known. However, a hydrate crystal, and a salt crystal of reduced glutathione are not known.